Unsteady Force Generation and Vortex Dynamics of Pitching and Plunging Flat Plates at Low Reynolds Number

摘要

An experimental investigation of pitching and plunging flat plate at a prescribed effective angle of attack in the St range of 0.16 to 0.32 and k range of 0.5 to 1.0 is presented. Force measurements and PIV technique were used to analyze and quantify the unsteady flow field created by the wing kinematics. A momentum-balance based non-intrusive force measurement technique and a systematic vortex detection algorithm were successfully implemented as a post-processing for PIV data to gain insight on the interplay between the unsteady force generation and vortex dynamics. It was determined that the inertia! effects, which are proportional to the St, dominate the unsteady force generation while the differences in the force generation for the same St kinematics are contributed by the circulatory effects such as the size and location of the leading edge vortex. The normal force with respect the flat plate was the primary contributor to the lift and drag production, and the projection of the normal force due to high pitch amplitude at higher St prompted higher thrust generation.